You don't need to do this with all Discus. Tank breed strains need to acclamated to "your" water just like any type of fish you get. RO water is not nessisary for these fish. As far as breeding goes again tank breed strains do not require RO water, however newly imported wild fish would benift from this and it would improve your chances of a successful spawn considerably. Some wild sp. of Discus are harder to breed than others, most domestic strains are not too diffacult to breed provided their needs are being met.
To answer your original question no you don't need RO water. If the fish was doing well and healthy in your LFS water chances your water is similar and they should be fine. Clean water and a stable water chemisry is better than trying to adjust it. You should be fine, keep doing your water changes and provide a healthy diet. Succesfully keeping domestic Discus isn't much more difficult than any other SA fish just remeber to keep the environment clean gravel vac at each water change and do regular maintenance on your filters. GL
